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Ecology and Epidemiology

Influence of Temperature, Moisture, Modified Gaseous Atmosphere, and Depth in Soil on Eruptive Sclerotial Germination of Sclerotium rolfsii. Z. K. Punja, Research scientist, Campbell Soup Company (also visiting assistant professor), Department of Plant Pathology, North Carolina State University, Raleigh 27695; S. F. Jenkins, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Phytopathology 74:749-754. Accepted for publication 6 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-749.

Eruptive sclerotial germination of Sclerotium rolfsii on Noble water agar or on the surface of unsterilized field soil was 80- 100% at 21- 30 C, at φ_s between - 2.5 and - 10 bars, and at φ_m between 0 and - 1 bar. Germination was not greatly reduced by CO₂ levels in the range of 0.5- 9%, O₂ levels between 15 and 20.5%, or C₂H₄ concentrations in the range of 1- 40 μg/ml. Sclerotial germination was nil at 9- 12 C, at φ_s <- 60 bars, at φ_m <- 10 bars (in a coarse sandy loam) or < - 15 bars (in a fine sandy loam), and at CO₂ and O₂ levels of >20 and <3%, respectively. Burial of sclerotia in moistened unsterile or autoclaved field soil at depths of >2.5 cm reduced germination and no sclerotia germinated at depths of >7 cm. This inhibition apparently was not the result of lack of aeration and may have been due in part to the direct or indirect effects of pressure imposed physically on the sclerotia by soil at the greater depths. Placing metal weights over sclerotia on the soil surface inhibited germination, and exudation of amino compounds and carbohydrates from these sclerotia was much greater than leakage from sclerotia without the simulated pressure from the weights. Reports of reduced survival of sclerotia deeper in soil could in part be explained by this increase in leakage, which enhanced colonization by soil microorganisms.